Recent biochemistry data shows that the C terminal tail (50 amino acids) of ion channel GluR2 interacts with the PDZ domain of adaptor protein GRIP and ATPase NSF mutually exclusively. Deletion mutants studies suggest that GRIP and NSF binds to two different stretches of GluR2 C-terminal tail (7 and 10 amino acids), respectively. How these interactions occlude each other is under investigation. A current model suggests a shielding effect: the motif for one interaction will be shielded once the other motif engages in the interaction already. We are trying to obtain and analyze the crystal structure of the GluR2, GRIP and GluR2, NSF complexes which will allow us to pinpoint structural bases for the motif shielding effect.